Pilot TMIE slot hopping

ABSTRACT

Embodiments are directed to systems, methods and computer program products for pilot time slot hopping to mitigate interference-based pilot time slot contamination. Embodiments include generating a multiple input multiple output (MIMO) system message frame structure comprising a header comprising a plurality of header time slots, an uplink (UL) time slot (optional), and a downlink (DL) time slot. Generating includes determining, based on a predetermined scheme, allocation of at least one of the plurality of header time slots to at least one user device within a predetermined area.

RELATED APPLICATION DATA

This application is a continuation of U.S. patent application Ser. No.14/413,382, filed Jan. 7, 2015, which is a national phase entry ofInternational Patent Application No. PCT/IB2014/060314, filed Mar. 31,2014, the disclosures of which are incorporated herein by reference intheir entireties.

BACKGROUND

The Third Generation Partnership Project (3GPP) radio access network(RAN) collaboration has addressed massive MIMO systems, and the proposedframe structure is a time division duplex (TDD) with a “header” timeslot for user equipment (UE) or user device pilot or training sequencetransmission, an uplink (UL) timeslot (optional) and a downlink (DL)timeslot.

BRIEF SUMMARY

Embodiments of the invention are directed to systems, methods andcomputer program products for pilot time slot hopping to mitigateinterference-based pilot time slot contamination. The method includesgenerating, using a processing device, a multiple input multiple output(MIMO) system message frame structure comprising a header comprising aplurality of header time slots, an uplink (UL) time slot (optional), anda downlink (DL) time slot, where generating comprises determining, basedon a predetermined scheme, allocation of at least one of the pluralityof header time slots to at least one user device within a predeterminedarea.

In some embodiments, the header is a user device training sequenceheader. In some embodiments, the header time slots are pilot time slots.

In some embodiments, one of a plurality of base stations (BSs) and/oraccess points (APs) comprises the processing device; and each of theplurality of BSs and/or APs are programmed for time synchronization ofthe frame structure such that each BS and/or AP recognizes when in timethe header occurs during MIMO system message transmission.

In some embodiments, generating the MIMO system message frame structurefurther comprises determining re-allocation, based on the predeterminedscheme, periodically of at least one of the plurality of header timeslots to at least one user device within the predetermined area. In somesuch embodiments, the re-allocation is determined periodically at leastevery millisecond.

In some embodiments, the method also includes determining, by theprocessing device, that interference-based pilot time slot contaminationmitigation is needed; and where generating the MIMO system message framestructure including determining allocation of the at least one of theplurality of header time slots to the at least one user device isperformed in response to the determination that interference-based pilottime slot contamination mitigation is needed. In some such embodiments,the method also includes determining, by the processing device, thatinterference-based pilot time slot contamination mitigation is notneeded; and based on the determination that interference-based pilottime slot contamination mitigation is not needed, maintaining presentallocation of the at least one of the plurality of header time slots tothe at least one user device.

In some embodiments, the method also includes, subsequent to generatingthe MIMO system message frame structure including determining allocationof the at least one of the plurality of header time slots to the atleast one user device, detecting, by the processing device, thatinterference-based pilot time slot contamination is occurring; and, inresponse to detecting that interference-based pilot time slotcontamination is occurring, determining re-allocation, based on thepredetermined scheme, of at least one of the plurality of header timeslots to at least one user device within the predetermined area in orderto mitigate the detected contamination.

In some embodiments, the plurality of header time slots comprises afirst plurality of header time slots and a second plurality of headertime slots; the first plurality of header time slots and the secondplurality of header time slots are different; and determining allocationof at least one of the plurality of header time slots to at least oneuser device comprises determining allocation of the first plurality ofheader time slots based on the predetermined scheme and withoutdetermining allocation of the second plurality of header time slotsbased on the predetermined scheme.

In some embodiments, generating the MIMO system message frame structurefurther comprises determining re-allocation, based on a secondpredetermined scheme, of at least one of the plurality of header timeslots to at least one user device within the predetermined area; andwherein (1) the second predetermined scheme is the same as the scheme,where the second scheme is initiated at a second start time differentfrom a start time of the scheme; or where the second scheme and thescheme both utilize the same pseudo-random pattern function but thesecond scheme utilizes at least one different seed than the scheme; or(2) the second predetermined scheme is different than the scheme.

In some embodiments, allocation is based on one of a plurality ofpredetermined schemes; generating the MIMO system message framestructure further comprises dynamically selecting, in order to avoidallocation of the same header time slots to multiple user devices, adifferent predetermined scheme for each re-allocation of header timeslots; determining re-allocation periodically and/or as needed to avoidcontamination, based on the dynamically selected predetermined scheme,of at least one of the plurality of header time slots to at least oneuser device within the predetermined area.

According to embodiments of the invention, an apparatus for pilot timeslot hopping to mitigate interference-based pilot time slotcontamination includes a memory; a processor; and a module stored in thememory, executable by the processor, and configured to generate amultiple input multiple output (MIMO) system message frame structurecomprising a header comprising a plurality of header time slots, anuplink (UL) time slot (optional), and a downlink (DL) time slot, wheregenerating comprises determining, based on a predetermined scheme,allocation of at least one of the plurality of header time slots to atleast one user device within a predetermined area.

In some embodiments, the apparatus is one of a plurality of basestations (BSs) and/or access points (APs); and each of the plurality ofBSs and/or APs are programmed for time synchronization of the framestructure such that each BS and/or AP recognizes when in time the headeroccurs during MIMO system message transmission.

In some embodiments, generating the MIMO system message frame structurefurther comprises determining re-allocation, based on the predeterminedscheme, periodically of at least one of the plurality of header timeslots to at least one user device within the predetermined area.

In some embodiments, the module is further configured to determine thatinterference-based pilot time slot contamination mitigation is needed;and where generating the MIMO system message frame structure includingdetermining allocation of the at least one of the plurality of headertime slots to the at least one user device is performed in response tothe determination that interference-based pilot time slot contaminationmitigation is needed.

In some embodiments, the module is further configured to, subsequent togenerating the MIMO system message frame structure including determiningallocation of the at least one of the plurality of header time slots tothe at least one user device, detect that interference-based pilot timeslot contamination is occurring; in response to detecting thatinterference-based pilot time slot contamination is occurring,determining re-allocation, based on the predetermined scheme, of atleast one of the plurality of header time slots to at least one userdevice within the predetermined area in order to mitigate the detectedcontamination.

In some embodiments, the plurality of header time slots comprises afirst plurality of header time slots and a second plurality of headertime slots; the first plurality of header time slots and the secondplurality of header time slots are different; and determining allocationof at least one of the plurality of header time slots to at least oneuser device comprises determining allocation of the first plurality ofheader time slots based on the predetermined scheme and withoutdetermining allocation of the second plurality of header time slotsbased on the predetermined scheme.

In some embodiments, generating the MIMO system message frame structurefurther comprises determining re-allocation, based on a secondpredetermined scheme, of at least one of the plurality of header timeslots to at least one user device within the predetermined area; and thesecond predetermined scheme is different than the scheme.

According to embodiments of the invention, a computer program productfor pilot time slot hopping to mitigate interference-based pilot timeslot contamination includes a non-transitory computer-readable mediumcomprising a set of codes for causing a computer to generate a multipleinput multiple output (MIMO) system message frame structure comprising aheader comprising a plurality of header time slots, an uplink (UL) timeslot (optional), and a downlink (DL) time slot, where generatingincludes determining, based on a predetermined scheme, allocation of atleast one of the plurality of header time slots to at least one userdevice within a predetermined area.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described embodiments of the invention in general terms,reference will now be made to the accompanying drawings, where:

FIG. 1 illustrates two UEs that are allocated difference pilot timeslots based on predetermined schemes according to embodiments of theinvention;

FIG. 2 illustrates an environment wherein user equipment devices andnetwork systems operate according to embodiments of the invention;

FIG. 3 illustrates a flowchart of a method 300 for pilot time slothopping to mitigate interference-based pilot time slot contaminationaccording to embodiments of the invention;

FIG. 4 illustrates a flowchart of another method 400 for pilot time slothopping to mitigate interference-based pilot time slot contaminationaccording to embodiments of the invention; and

FIG. 5 illustrates a flowchart of another method 500 for pilot time slothopping to mitigate interference-based pilot time slot contaminationaccording to embodiments of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Embodiments of the present invention now may be described more fullyhereinafter with reference to the accompanying drawings, in which some,but not all, embodiments of the invention are shown. Indeed, theinvention may be embodied in many different forms and should not beconstrued as limited to the embodiments set forth herein; rather, theseembodiments are provided so that this disclosure may satisfy applicablelegal requirements. Like numbers refer to like elements throughout.

As mentioned above, in massive MIMO systems, the proposed framestructure is TDD with a “header”, UL and DL. For efficient networktransmission, the header or pilot time slots for multiple UEs should beorthogonal (non-overlapping). This may be difficult because the pilottime slot space or time allocation is limited. One option is to achieveorthogonality by assigning a time slot within the header for each uniqueUE in a particular area, such as a cell. However, the limited number oftime slots, particularly in densely populated cells, may require thattime slots are reused for multiple UEs. Further, in some unlicensedbands, reuse of time slots may be required. Thus, when two or more UEsaccidentally or inadvertently use the same header time slot,interference will occur, such as channel state information (CSI)interference and inaccuracies.

Accordingly, embodiments of the invention are directed to systems,methods and computer program products for pilot time slot hopping tomitigate interference-based pilot time slot contamination. Embodimentsinclude generating a multiple input multiple output (MIMO) systemmessage frame structure comprising a header comprising a plurality ofheader time slots, an uplink (UL) time slot (optional), and a downlink(DL) time slot. Generating includes determining, based on apredetermined scheme, allocation of at least one of the plurality ofheader time slots to at least one user device within a predeterminedarea. The scheme may be or include a pseudo-random scheme, a cyclicscheme, a non-random scheme, an orthogonal scheme and/or the like.

Referring now to FIG. 1, diagram illustrates a MIMO system message framestructure where UE1 and UE2 have been allocated different time slotswithin the header for each training sequence according to embodiments ofthe invention. As shown, for each training sequence, the time slotsallocated to UE1 and UE2 do not overlap and therefore, orthogonality isachieved.

Referring now to FIG. 2, a network environment 200 is illustrated inaccordance with one embodiment of the present invention. As illustratedin FIG. 2, the network system 208 is operatively coupled, via a network201 to the user equipment 204 and/or 206. In this configuration, thenetwork system 208 may send information to and receive information fromthe user equipment devices 204 and/or 206. FIG. 2 illustrates only oneexample of an embodiment of a network environment 200, and it will beappreciated that in other embodiments one or more of the systems,devices, or servers may be combined into a single system, device, orserver, or be made up of multiple systems, devices, or servers.

The network 201 may be a global area network (GAN), such as theInternet, a wide area network (WAN), a local area network (LAN), atelecommunication network or any other type of network or combination ofnetworks. The network 201 may provide for wireline, wireless, or acombination wireline and wireless communication between devices on thenetwork 201. In some embodiments, the users 202 and 205 are individualswho maintain cellular products with one or more providers.

As illustrated in FIG. 2, the network system 208 generally comprises acommunication device 246, a processing device 248, and a memory device250. As used herein, the term “processing device” generally includescircuitry used for implementing the communication and/or logic functionsof the particular system. For example, a processing device may include adigital signal processor device, a microprocessor device, and variousanalog-to-digital converters, digital-to-analog converters, and othersupport circuits and/or combinations of the foregoing. Control andsignal processing functions of the system are allocated between theseprocessing devices according to their respective capabilities. Theprocessing device may include functionality to operate one or moresoftware programs based on computer-readable instructions thereof, whichmay be stored in a memory device.

The processing device 248 is operatively coupled to the communicationdevice 246 and the memory device 250. The processing device 248 uses thecommunication device 246 to communicate with the network 201 and otherdevices on the network 201. As such, the communication device 246generally comprises a modem, server, or other device for communicatingwith other devices on the network 201.

As further illustrated in FIG. 2, the network system 208 comprisescomputer-readable instructions 254 stored in the memory device 250,which in one embodiment includes the computer-readable instructions 254of an application 258 including instructions for performing one or moreprocesses and/or method steps discussed herein and/or one or moreprocesses and/or method steps not discussed herein. In some embodiments,the memory device 250 includes data storage 252 for storing data relatedto and/or used by the application 258.

As illustrated in FIG. 2, the user equipment 206 (or user device)generally comprises a communication device 236, a processing device 238,and a memory device 240. The processing device 238 is operativelycoupled to the communication device 236 and the memory device 240. Insome embodiments, the processing device 238 may send or receive datafrom the user equipment 204, and/or the network system 208 via thecommunication device 236 over a network 201. As such, the communicationdevice 236 generally comprises a modem, server, or other device forcommunicating with other devices on the network 201.

As further illustrated in FIG. 2, the user equipment 206 comprisescomputer-readable instructions 242 stored in the memory device 240,which in one embodiment includes the computer-readable instructions 242of an application 244 including instructions for performing one or moreprocesses and/or method steps discussed herein and/or one or moreprocesses and/or method steps not discussed herein.

It is understood that the servers, systems, and devices described hereinillustrate one embodiment of the invention. It is further understoodthat one or more of the servers, systems, and devices can be combined inother embodiments and still function in the same or similar way as theembodiments described herein.

Referring now to FIG. 3, a flowchart illustrates a method 300 for pilottime slot hopping to mitigate interference-based pilot time slotcontamination according to embodiments of the invention. The first stepof method 300, as represented by block 310, is generating, using aprocessing device (such as a processing device of a base station oraccess point), a multiple input multiple output (MIMO) system messageframe structure. The frame structure includes a header comprising aplurality of header time slots, an uplink (UL) time slot, and a downlink(DL) time slot. In some embodiments, the frame structure only includespilot and DL time slots and does not include UL time slots. Accordingly,such frames include no payload and may be utilized for UEs in idle mode.

Generating the message frame structure, as represented by block 320,includes determining, based on a predetermined scheme, allocation of atleast one of the plurality of header time slots to at least one userdevice within a predetermined area. The scheme may be pseudo-random,cyclical, non-random, orthogonal and/or the like. In some cases, theheader is a UE training sequence header and it may be called a pilottime slot.

Various embodiments discussed herein assume that all base stations (BSs)and/or access points (APs) are synchronized such that they know when theheader, UL and DL slots occur. In one example, each of the plurality ofBSs and/or APs are preprogrammed for time synchronization of the framestructure such that each BS and/or AP recognizes when in time the headeroccurs during MIMO system message transmission. In other embodiments,the BS/APs are contemporaneously programmed based on a feature, method,algorithm, process, application or the like.

In various embodiments, the BS/AP allocates the pattern, but in otherembodiments, each UE selects a pattern and a UE-ID is included in thepilot time slot. Orthogonal hopping patterns might be generated indifferent ways. For example, in some cases different random patterns areselected as discussed above. However, in other cases, the same patternmay be used with each UE selecting or being allocated (by a BS/AP)different start points or the same “random pattern function” but withdifferent seeds.

In some embodiments, the method 300 includes periodically determiningre-allocation, based on the predetermined scheme, of at least one of theplurality of header time slots to at least one user device within thepredetermined area, as represented by block 330. In some suchembodiments, re-allocation may be periodically determined at least everymillisecond.

Referring now to FIG. 4, a method 400 includes some steps that may beincluded with the steps discussed with reference to method 300 of FIG. 3according to embodiments of the invention. First, as represented byblock 410, the system determines whether interference-based pilot timeslot contamination mitigation is needed. This may be done by detectingwhether contamination or interference of transmission is occurring onthe network. The system may determine contamination is occurring in avariety of ways. For example, pilot contamination will cause increasedBER (bit error state), SNR (signal to noise and interferer ratio)degradation or contamination may possibly be detected in the footprint.Applying time slot hopping might mitigate such contamination by itselfor may require additional methods for effective contaminationmitigation. Accordingly, other tools may be used in conjunction with thetime hopping methods disclosure herein to improve communication. Suchother methods that might be used in conjunction include frequency bandre-selection, synchronization to neighbor cells, applying additionalmultiple access (MA) method(s) and/or applying spreading (coding),and/or changing modulation scheme(s) for higher robustness. In somecases, synchronization might be required in order for hopping to assistin mitigation of contamination, therefore requiring pairing with anothermethod in some cases. For example, if a UE or BS/AP detects high BER andattempts to change the pilot time slot (based on a standard time slotallocation) without improving the high BER, time slot hopping can beactivated and average BER may thereby improve.

If mitigation is needed, as represented by block 420, generating theMIMO system message frame structure includes determining allocation ofthe at least one of the plurality of header time slots to the at leastone UE. In other words, allocation of the header time slots to the UEsmay be performed in response to a determination that contaminationmitigation is needed.

If it is determined that mitigation is not needed, as represented byblock 430, the method includes maintaining present allocation of theheader time slots to the UEs. In other words, the system may maintainthe current time slot allocation in response to determining that nocontamination mitigation is necessary. The system may determine thatcontamination is not occurring (or is not likely to occur) by measuringmetrics described above such as the BER. If one or more of such metricsare better, time slot hopping may be deactivated. In some cases, one ormore of the metrics are continually (or periodically) monitoredwhen/while time slot hopping is deactivated, and if it is determinedthat one or more of the metrics is not meeting desired thresholds orstandards, then time hopping may then be reactivated. For example, thesystem may detect that there is high BER on only some frames when acollision occurs. In such a cases, the system may deactivate time slothopping and finding/allocating an open or “free” time slot may provemore economical and/or efficient.

In some embodiments, the method includes detecting thatinterference-based pilot time slot contamination is occurring aftergenerating the MIMO system message frame structure (see step 310. Then,in response to detecting that contamination is occurring with theoriginally allocated time slots, the method then determinesre-allocation. The re-allocation may be based on the same predeterminedscheme that was used in the original allocation.

In some embodiments, allocation based on predetermined (or dynamicallyselected) schemes is only applied to one or more sub-sets of the entireset of pilot time slots. In other words, the plurality of header timeslots may be broken into a first plurality of header time slots and asecond plurality of header time slots, where the first plurality ofheader time slots and the second plurality of header time slots aredifferent. In these embodiments, the allocation of one of the sub-setsof time slots may be determined based on the predetermined (ordynamically selected) scheme and allocation of the other sub-set(s) maybe based on some other scheme, such as a simple assignment of time slotsto UEs.

In some embodiments, the system uses different patterns or schemesdynamically selected in order to avoid using the same schemes. Then, asrepresented by block 520, the system may determine re-allocation basedon a second predetermined scheme that is different than the originallyused scheme.

Referring now to FIG. 5, a method 500 includes steps that may beincluded with the steps discussed with reference to method 300 of FIG.3. In some cases, allocation is based on one of a plurality ofpredetermined schemes. Generating the message frame structure mayinclude dynamically selecting, in order to avoid allocation of the sameheader time slots to multiple user devices, a different predeterminedscheme for each re-allocation of header time slots, as represented byblock 510. Then, the system determines re-allocation periodically and/oras needed to avoid contamination, based on the dynamically selectedpredetermined scheme, as represented by block 520.

When there are many UEs connected to a single B S or AP within a singlecell, various embodiments of the invention enable orthogonal allocationof pilot time slots using pilot time slot hopping methods discussedherein. Thus, a possible contamination from a neighboring cell may havethe same system impact but will not harm only a single UE'stransmissions. Further, introduction of time slot hopping has little orno throughput cost.

Although many embodiments of the present invention have just beendescribed above, the present invention may be embodied in many differentforms and should not be construed as limited to the embodiments setforth herein; rather, these embodiments are provided so that thisdisclosure will satisfy applicable legal requirements. Also, it will beunderstood that, where possible, any of the advantages, features,functions, devices, and/or operational aspects of any of the embodimentsof the present invention described and/or contemplated herein may beincluded in any of the other embodiments of the present inventiondescribed and/or contemplated herein, and/or vice versa. In addition,where possible, any terms expressed in the singular form herein aremeant to also include the plural form and/or vice versa, unlessexplicitly stated otherwise. As used herein, “at least one” shall mean“one or more” and these phrases are intended to be interchangeable.Accordingly, the terms “a” and/or “an” shall mean “at least one” or “oneor more,” even though the phrase “one or more” or “at least one” is alsoused herein. Like numbers refer to like elements throughout.

As will be appreciated by one of ordinary skill in the art in view ofthis disclosure, the present invention may include and/or be embodied asan apparatus (including, for example, a system, machine, device,computer program product, and/or the like), as a method (including, forexample, a business method, computer-implemented process, and/or thelike), or as any combination of the foregoing. Accordingly, embodimentsof the present invention may take the form of an entirely businessmethod embodiment, an entirely software embodiment (including firmware,resident software, micro-code, stored procedures in a database, etc.),an entirely hardware embodiment, or an embodiment combining businessmethod, software, and hardware aspects that may generally be referred toherein as a “system.” Furthermore, embodiments of the present inventionmay take the form of a computer program product that includes acomputer-readable storage medium having one or more computer-executableprogram code portions stored therein. As used herein, a processor, whichmay include one or more processors, may be “configured to” perform acertain function in a variety of ways, including, for example, by havingone or more general-purpose circuits perform the function by executingone or more computer-executable program code portions embodied in acomputer-readable medium, and/or by having one or moreapplication-specific circuits perform the function.

It will be understood that any suitable computer-readable medium may beutilized. The computer-readable medium may include, but is not limitedto, a non-transitory computer-readable medium, such as a tangibleelectronic, magnetic, optical, electromagnetic, infrared, and/orsemiconductor system, device, and/or other apparatus. For example, insome embodiments, the non-transitory computer-readable medium includes atangible medium such as a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), a compact discread-only memory (CD-ROM), and/or some other tangible optical and/ormagnetic storage device. In other embodiments of the present invention,however, the computer-readable medium may be transitory, such as, forexample, a propagation signal including computer-executable program codeportions embodied therein.

One or more computer-executable program code portions for carrying outoperations of the present invention may include object-oriented,scripted, and/or unscripted programming languages, such as, for example,Java, Perl, Smalltalk, C++, SAS, SQL, Python, Objective C, JavaScript,and/or the like. In some embodiments, the one or morecomputer-executable program code portions for carrying out operations ofembodiments of the present invention are written in conventionalprocedural programming languages, such as the “C” programming languagesand/or similar programming languages. The computer program code mayalternatively or additionally be written in one or more multi-paradigmprogramming languages, such as, for example, F#.

Some embodiments of the present invention are described herein withreference to flowchart illustrations and/or block diagrams of apparatusand/or methods. It will be understood that each block included in theflowchart illustrations and/or block diagrams, and/or combinations ofblocks included in the flowchart illustrations and/or block diagrams,may be implemented by one or more computer-executable program codeportions. These one or more computer-executable program code portionsmay be provided to a processor of a general purpose computer, specialpurpose computer, and/or some other programmable data processingapparatus in order to produce a particular machine, such that the one ormore computer-executable program code portions, which execute via theprocessor of the computer and/or other programmable data processingapparatus, create mechanisms for implementing the steps and/or functionsrepresented by the flowchart(s) and/or block diagram block(s).

The one or more computer-executable program code portions may be storedin a transitory and/or non-transitory computer-readable medium (e.g., amemory, etc.) that can direct, instruct, and/or cause a computer and/orother programmable data processing apparatus to function in a particularmanner, such that the computer-executable program code portions storedin the computer-readable medium produce an article of manufactureincluding instruction mechanisms which implement the steps and/orfunctions specified in the flowchart(s) and/or block diagram block(s).

The one or more computer-executable program code portions may also beloaded onto a computer and/or other programmable data processingapparatus to cause a series of operational steps to be performed on thecomputer and/or other programmable apparatus. In some embodiments, thisproduces a computer-implemented process such that the one or morecomputer-executable program code portions which execute on the computerand/or other programmable apparatus provide operational steps toimplement the steps specified in the flowchart(s) and/or the functionsspecified in the block diagram block(s). Alternatively,computer-implemented steps may be combined with, and/or replaced with,operator- and/or human-implemented steps in order to carry out anembodiment of the present invention.

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive on the broad invention, andthat this invention not be limited to the specific constructions andarrangements shown and described, since various other changes,combinations, omissions, modifications and substitutions, in addition tothose set forth in the above paragraphs, are possible. Those skilled inthe art will appreciate that various adaptations, modifications, andcombinations of the just described embodiments can be configured withoutdeparting from the scope and spirit of the invention. Therefore, it isto be understood that, within the scope of the appended claims, theinvention may be practiced other than as specifically described herein.

What is claimed is:
 1. A method for managing multiple input multipleoutput (MIMO) system messages in a massive MIMO system, each MIMO systemmessage having a header with a header frame structure comprising asequence of plural header time slots, the method comprising: (a)allocating one of the plurality of header time slots as a pilot signaltime slot to a first user device that operates in the massive MIMOsystem; (b) monitoring a metric indicative of pilot contaminationbetween the first user device and a second user device, wherein (i) ifthe metric does not indicate the pilot contamination, then maintainingthe header time slot allocation of (a) for consecutive MIMO systemmessages or (ii) if the metric does indicate the pilot contamination,then: (c) activating pilot time slot hopping, the pilot time slothopping comprising reallocating the pilot signal time slot allocated tothe first user device in (a) to a different header time slot in thesequence of plural header time slots; and (d) determining that pilotcontamination mitigation is no longer needed and deactivating the pilottime slot hopping so that the header time slot allocation at the time ofdeactivating the pilot time slot hopping is maintained for consecutiveMIMO system messages.
 2. The method of claim 1, wherein the reallocatingof (c) is carried out periodically until (d) is carried out.
 3. Themethod of claim 2, wherein the reallocating of (c) is carried out everymillisecond until (d) is carried out.
 4. The method of claim 1, whereinthe reallocating of (c) is carried out for each MIMO system messageuntil (d) is carried out.
 5. The method of claim 1, further comprising,in (a), allocating another of the plurality of header time slots as apilot signal time slot to the second user device that operates in themassive MIMO system, the header time slots respectively allocated to thefirst and second user devices as pilot signal time slots being differentheader time slots of the sequence of plural header time slots; andwherein (c) is carried out without reallocating the pilot signal timeslot allocated to the second user device.
 6. The method of claim 1,wherein the allocation of (a) to the first user device is carried outusing a predetermined one of plural allocation schemes.
 7. The method ofclaim 6, wherein the reallocating of (c) is carried out with thepredetermined one of the plural allocation schemes used to carry out theallocation of (a).
 8. The method of claim 6, wherein the reallocating of(c) is carried out using another of the plural allocation schemes. 9.The method of claim 6, wherein the reallocating of (c) is carried outusing one of the plural allocation schemes that is dynamically selected.10. The method of claim 1, wherein the method is carried out by anetwork access node of the massive MIMO system with which the first andsecond user devices communicate.
 11. The method of claim 1, wherein theheader is a user device training sequence header.
 12. A massive multipleinput multiple output (MIMO) network access node in a massive MIMOsystem, the network access node managing system messages in the massiveMIMO system, each MIMO system message having a header with a headerframe structure comprising a sequence of plural header time slots, thenetwork access node comprising: a memory; at least one processor; and amodule stored in the memory, executable by the at least one processor,and configured to: (a) allocate one of the plurality of header timeslots as a pilot signal time slot to a first user device that operatesin the massive MIMO system; (b) monitor a metric indicative of pilotcontamination between the first user device and a second user device,wherein (i) if the metric does not indicate the pilot contamination,then maintain the header time slot allocation of (a) for consecutiveMIMO system messages or (ii) if the metric does indicate the pilotcontamination, then: (c) activate pilot time slot hopping, the pilottime slot hopping comprising reallocating the pilot signal time slotallocated to the first user device in (a) to a different header timeslot in the sequence of plural header time slots; and (d) determine thatpilot contamination mitigation is no longer needed and deactivate thepilot time slot hopping so that the header time slot allocation at thetime of deactivating the pilot time slot hopping is maintained forconsecutive MIMO system messages.
 13. The massive MIMO network accessnode of claim 12, wherein the reallocating of (c) is carried outperiodically until (d) is carried out.
 14. The massive MIMO networkaccess node of claim 13, wherein the reallocating of (c) is carried outevery millisecond until (d) is carried out.
 15. The massive MIMO networkaccess node of claim 12, wherein the reallocating of (c) is carried outfor each MIMO system message until (d) is carried out.
 16. The massiveMIMO network access node of claim 12, wherein the module is furtherconfigured, in (a), to allocate another of the plurality of header timeslots as a pilot signal time slot to the second user device thatoperates in the massive MIMO system, the header time slots respectivelyallocated to the first and second user devices as pilot signal timeslots being different header time slots of the sequence of plural headertime slots; and wherein (c) is carried out without reallocating thepilot signal time slot allocated to the second user device.
 17. Themassive MIMO network access node of claim 12, wherein the allocation of(a) to the first user device is carried out using a predetermined one ofplural allocation schemes.
 18. The massive MIMO network access node ofclaim 17, wherein the reallocating of (c) is carried out with thepredetermined one of the plural allocation schemes used to carry out theallocation of (a).
 19. The massive MIMO network access node of claim 17,wherein the reallocating of (c) is carried out using another of theplural allocation schemes.
 20. The massive MIMO network access node ofclaim 17, wherein the reallocating of (c) is carried out using one ofthe plural allocation schemes that is dynamically selected.
 21. Themassive MIMO network access node of claim 12, wherein the header is auser device training sequence header.